.help dcmpf Jun99 "Slalib Package"
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      SUBROUTINE slDCMF (COEFFS,XZ,YZ,XS,YS,PERP,ORIENT)

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      D C M F
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  Decompose an [X,Y] linear fit into its constituent parameters:
  zero points, scales, nonperpendicularity and orientation.

  Given:
     COEFFS  d(6)      transformation coefficients (see note)

  Returned:
     XZ       d        x zero point
     YZ       d        y zero point
     XS       d        x scale
     YS       d        y scale
     PERP     d        nonperpendicularity (radians)
     ORIENT   d        orientation (radians)

  The model relates two sets of [X,Y] coordinates as follows.
  Naming the elements of COEFFS:

     COEFFS(1) = A
     COEFFS(2) = B
     COEFFS(3) = C
     COEFFS(4) = D
     COEFFS(5) = E
     COEFFS(6) = F

  the model transforms coordinates [X1,Y1] into coordinates
  [X2,Y2] as follows:

     X2 = A + B*X1 + C*Y1
     Y2 = D + E*X1 + F*Y1

  The transformation can be decomposed into four steps:

     1)  Zero points:

             x' = XZ + X1
             y' = YZ + Y1

     2)  Scales:

             x'' = XS*x'
             y'' = YS*y'

     3)  Nonperpendicularity:

             x''' = cos(PERP/2)*x'' + sin(PERP/2)*y''
             y''' = sin(PERP/2)*x'' + cos(PERP/2)*y''

     4)  Orientation:

             X2 = cos(ORIENT)*x''' + sin(ORIENT)*y'''
             Y2 =-sin(ORIENT)*y''' + cos(ORIENT)*y'''

  See also slFTXY, slPXY, slINVF, slXYXY

  P.T.Wallace   Starlink   14 August 1994

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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